1. Field of the Invention
The present application relates generally to rotary aircraft, and more particularly, to tail booms for helicopters.
2. Description of Related Art
Conventional helicopters typically include one or more main rotors situated above a fuselage and an engine disposed within the fuselage for rotating the main rotor. During operation, the engine exerts a torque on the fuselage (“fuselage torque”), which causes the fuselage to rotate in a direction opposite to that of the main rotor rotational movement. Fuselage torque is greatest during high power operation, namely, during very low or very high speed flight.
During operation at low forward speeds, downwash is at its maximum, thus requiring greater torque control to counteract the fuselage torque. Tail rotors are effective anti-torque devices for controlling fuselage torque during takeoff, landing, and during low forward speed flight. FIG. 1 shows a conventional helicopter 1 comprising a main rotor 2 situated above the fuselage and a tail rotor 4 attached to the aft section of the fuselage via a tail boom 3. The tail rotor and associated drive system must be sized for the low speed regime. As a result, the tail rotor is generally larger and heavier than needed in other flight regimes and produces additional drag and power penalties at high speeds. These factors are cumulative and all result in degradation of helicopter performance.
Some conventional helicopters include strakes, fins, and/or other suitable devices for controlling the fuselage torque. During high speed flight, the torque control can be provided by aerodynamic surfaces, such as fins. However, during low speed flight, these surfaces are ineffective. FIG. 2 illustrates a cross-sectional view of tail boom 3 of helicopter 1. Auxiliary wings 5A and 5B extend alongside the outer surface of tail boom 3 for directing the downward rotorwash in a lateral direction relative to the tail boom. Wings 5A and 5B redirect the rotorwash in a lateral direction relative to the tail boom. Strakes and fins are effective means for counteracting the fuselage torque; however, strakes and fins increase the overall weight of the aircraft, which in turn, requires the main rotor to create additional lift to compensate for the added weight. In addition, the added weight decreases the lifting capacity of the aircraft. Furthermore, strakes and fins include the additional download penalty associated with higher vertical drag from the rotorwash.
Other helicopters include circulation control tail booms comprising one or more inner ducts disposed within the tail boom for channeling exhaust and/or other types of engine-driven fluid through the tail boom. The channeled fluid exits the tail boom through one or more exit ports in a lateral direction relative to the tail boom. The circulation tail boom provides sufficient anti-torque to completely eliminate the need for a tail rotor; however, the tail boom significantly increase the overall weight of the helicopter, thereby increasing the power consumption and rendering the design ineffective in most applications.
Although the foregoing developments represent great strides in the area of anti-torque devices for a helicopter, many shortcomings remain.
While the tail boom of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the process of the present application as defined by the appended claims.